Research output: Contribution to journal › Article › peer-review

Original language | English |
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Pages (from-to) | 1016-1032 |

Journal | Monthly Notices of the Royal Astronomical Society |

Volume | 407 |

Issue number | 2 |

Publication status | Published - 1 Sep 2010 |

We present results on the evolution of the intrinsic scatter of black
hole masses considering different implementations of a model in which
black holes only grow via mergers. We demonstrate how merger driven
growth affects the correlations between black hole mass and host bulge
mass. The simple case of an initially lognormal distributed scatter in
black hole and bulge masses combined with random merging within the
galaxy population results in a decreasing scatter with merging
generation/number as predicted by the central-limit theorem. In general
we find that the decrease in scatter σ is well approximated by
σmerg(m) ~ σini × (m + 1)-
a/2 with a = 0.42 for a range of mean number of mergers m <50.
For a large mean number of mergers (m > 100) we find a convergence to
a = 0.61. This is valid for a wide range of different initial
distributions, refill-scenarios or merger mass ratios. Growth scenarios
based on halo merger trees of a (100Mpc)3
ΛCDM-simulation show a similar behaviour with a scatter decrease
of a = 0.30 with typical number of mergers m <50 consistent with
random merging (best matching model: a = 0.34). Assuming a present-day
scatter of 0.3 dex in black hole mass and a mean number of mergers not
exceeding m = 50 our results imply a scatter of 0.6 dex at z = 3 and
thus a possible scenario in which overmassive (and undermassive) black
holes at high redshift are a consequence of a larger intrinsic scatter
in black hole mass. A simple toy model connecting the growth of black
holes to the growth of ΛCDM haloes via mergers, neglecting any
contribution from accretion, yields a consistent
M•-MBulge relation at z = 0 - if we assume
the correct initial relation.

- methods: numerical, methods: statistical, galaxies: bulges, galaxies: evolution

ID: 11176019